The earliest instances of relatively prolonged cardiac stimulation, namely cardiac pacing, of a patient's heart was effected through implanted cardiac leads attached to the heart muscle at distal electrode ends and extending through an incision in the patient's skin. To effect unipolar pacing of the heart, a single such implantable pacing lead was employed in conjunction with a subcutaneously implanted or skin-surface attached return electrode coupled to an external lead conductor. To effect bipolar pacing of the heart, two such implantable pacing leads were implanted with the electrode ends implanted a distance apart. The attachment of the proximal ends of the lead conductors to the temporary cardiac pacemaker connector elements was initially effected by simply stripping insulation from the proximal conductor ends, and inserting and securing the bare conductor ends in transverse openings in threaded posts. Later, finished connector pins were formed at the proximal connector ends of the lead bodies that could be inserted into the end openings of thumb nuts and connector posts.
Implantable pacing leads evolved into permanent, unipolar and bipolar, endocardial and epicardial, pacing leads for chronic implantation in a patient. The proximal electrical connector assemblies were then connected with connector elements of a totally implanted, cardiac pacemaker pulse generator. To withstand stress, implantable pacing lead conductors were formed of coiled wire and inserted within an insulative lead body lumen, thereby providing a coiled wire lumen that was sized to receive a stiffening stylet wire to assist tranvenous implantation of the endocardial pacing leads. The proximal end of the coiled wire conductor was attached to a tubular connector pin at the terminus of the lead connector and shaped to be received in the connector assembly of the implantable pacemaker pulse generator. In the case of endocardial permanent pacing leads, the connector or pin was formed with a lumen therein aligned with the coiled wire lumen so that the stiffening stylet wire could be inserted down the length of the lead body during the transvenous introduction and withdrawn after placement of the distal electrode was achieved. Many of these features are employed in current permanent pacing leads.
More recently, bipolar and multi-polar permanently implantable pacing leads and leads for use in pacing and cardioversion/defibrillation (collectively referred to as permanent implantable cardiac leads) have been developed using coaxially arranged, coiled wire conductors and/or parallel-wound, multi-filar coiled wire conductors. In the case of endocardial cardiac leads, the stylet wire lumen is employed to receive the stiffening stylet wire for implantation as described above. The proximal connector end assemblies are formed with at least two spaced apart lead connector elements arranged in-line from a proximal lead connector pin to at least one or more distally located ring-shaped element or lead connector ring. Typical bipolar in-line lead connector assemblies for multi-filar, coiled wire conductors are shown, for example, in commonly assigned U.S. Pat. Nos. 4,944,088 and 4,951,687 and 5,007,435, respectively, the teachings of which are hereby incorporated by reference.
Unipolar and bipolar, temporary endocardial pacing leads and temporary epicardial heart wires were also developed for implantation of the distal electrode(s) thereof in contact with the endocardium or sutured through the epicardium of the hearts of hospitalized patients. The lead body size of these temporary pacing leads and heart wires has typically been smaller than that of permanent cardiac leads because of the absence of an internal wire coil lumen for receiving a stylet wire. Still, in the case of bipolar temporary pacing leads and heart wires, either a lead connector pin and ring set are employed providing a pair of lead connector pins.
During or after implantation of the implantable cardiac lead(s), an external pacing system analyzer (PSA), e.g. MEDTRONIC® Model No.'s 2290 and 8090, is attached to the proximal lead connector end assembly accessible through the incision to assess the performance of the system and verify proper lead placement. It is necessary in some cases to use either a disposable or a reusable “surgical cable” adaptor to complete the connection between the implanted lead and the external pacing system analyzer.
Some patient and surgical cable adaptors constitute a connector assembly at a first end that is compatible with the PSA or temporary pacemaker terminals, a cable including conductors extending from the first end to a second end, and lead connector element connectors at the second end. Typically, two to four conductors are included in the cable, and a set of two or four alligator clips are provided at the second end for attachment to one or more lead connector rings and a pin of one or two implantable cardiac leads.
In the case of a permanent pacing lead having a stylet wire fitted within the lead lumen and projecting out proximally through the connector pin, alligator clips are utilized that attach across the connector rings and pins. However, such an attachment is not as secure and electrically isolated as would be desirable. It is undesirable to either lose the connection or to allow an electrical static discharge or other shock or impulse to reach the heart through the exposed lead connector ends. Furthermore, it has been observed that the careless use of alligator clips can damage the insulation sheathes adjacent to the lead connector end ring or connector pins. This problem is further complicated in the case of leads having a plurality of contact rings separated by insulative sealing surfaces. That is, not only is there a potential for shorting between alligator clips and/or test probes, but such clips may cause damage to the insulation/sealing areas adjacent the contact rings.